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  • 1. Diez, Beatriz
    et al.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    El-Shehawy, Rehab
    Marine diazotrophic cyanobacteria: out of the blue.2008In: Plant Biotechnology, ISSN 1342-4580, Vol. 25, no 3, p. 221-225Article, review/survey (Other (popular science, discussion, etc.))
  • 2.
    Jonasson, Sara
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Vintila, Simina
    Stockholm University, Faculty of Science, Department of Botany.
    Sivonen, Kaarina
    El-Shehawy, Rehab
    Stockholm University, Faculty of Science, Department of Botany.
    Expression of the nodularin synthetase genes in the Baltic Sea bloom-former cyanobacterium Nodularia spumigena strain AV1.2008In: FEMS Microbiol Ecol, ISSN 0168-6496, Vol. 65, no 1, p. 31-39Article in journal (Refereed)
    Abstract [en]

    Cyanobacterial blooms in the Baltic Sea are a common phenomenon and are formed by the heterocystous, filamentous species Nodularia spumigena. The toxicity of these blooms is attributed to the hepatotoxin nodularin, produced by N. spumigena. Little is known regarding the regulatory mechanisms or environmental signaling that control nodularin production. Here we report the characterization of the transcriptional expression pattern of the nodularin synthetase gene cluster (nda) during phosphate depletion, and nitrogen supplementation. Real-time PCR analysis of these genes revealed that while cells continuously expressed the nda cluster, the expression of all nda genes increased when cells were subjected to phosphate depletion, and decreased in the presence of ammonium. In contrast to the shifts in expression, the intracellular and extracellular nodularin concentrations did not vary significantly during the treatments.

  • 3. Moron-Lopez, Jesus
    et al.
    Nieto-Reyes, Lucia
    Aguado, Sonia
    El-Shehawy, Rehab
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. IMDEA Water Institute, Spain.
    Molina, Serena
    Recycling of end-of-life reverse osmosis membranes for membrane biofilms reactors (MBfRs). Effect of chlorination on the membrane surface and gas permeability2019In: Chemosphere, ISSN 0045-6535, E-ISSN 1879-1298, Vol. 231, p. 103-112Article in journal (Refereed)
    Abstract [en]

    Reducing human impacts on drinking water is one of the main challenges for the water treatment industry. This work provides new results to support the recycling of EoL desalination reverse osmosis (RO) membranes for Membranes Biofilm Reactors (MBfRs). We investigate if the controlled-removal of fouling and polyamide layer may favor the use of these membranes in MBfRs. It also would allow establishing a normalized methodology of membrane recycling, regardless of inherited fouling during its lifespan. For this purpose, we transform by chlorination discarded brackish (BWd) and seawater (SWd) membranes into nanofiltration (BWt-NF and SWt-NF) and ultrafiltration (BWt-UF and SWt-UF) membranes. Our results show that chlorine attacks allow the fouling cleaning while improves the hydrophilicity and maintains roughness only in BWt-NF. Therefore, the bacterial deposition in this membrane is greater than the other tested membranes. Besides, the microcystin (MC) degradation capacity of BWt-NF verifies the compatibility of the chemical modification for the biological activity of MC-degrading bacteria. Finally, our results also provide that polyamide thin-film composite (PA-TFC) membranes, originally manufactured for salt rejection during desalination processes, offer competitive gases diffusion at low pressures. Therefore, we conclude that the membrane recycling may provide alternative low cost and gas permeable membranes for MBfRs, according to circular economy principles.

  • 4. Morón-López, Jesús
    et al.
    Nieto-Reyes, Lucia
    Senan-Salinas, Jorge
    Molina, Serena
    El-Shehawy, Rehab
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. IMDEA Water Institute, Spain.
    Recycled desalination membranes as a support material for biofilm development: A new approach for microcystin removal during water treatment2019In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 647, p. 785-793Article in journal (Refereed)
    Abstract [en]

    Increased harmful cyanobacterial blooms and drought are some negative impacts of global warming. To deal with cyanotoxin release during water treatment, and to manage the massive quantities of end-of-life membrane waste generated by desalination processes, we propose an innovative biological system developed from recycled reverse osmosis (RO) membranes to remove microcystins (MC). Our system, named the Recycled-Membrane Biofilm Reactor (R-MBfR), effectively removes microcystins, while reducing the pollution impact of RO membrane waste by prolonging their life span at the same time. This multidisciplinary work showed that the inherent flaw of RO membranes, i.e., fouling, can be considered an advantageous characteristic for biofilm attachment. Factors such as roughness, hydrophilic surfaces, and the role of calcium in cell-cell and cell-surface interactions, encouraged bacterial growth on discarded membranes. Biofilm development was stimulated by using a laboratory-scale membrane module simulator cell. The R-MBfR proved versatile and was capable of degrading 2 mg center dot L-1 of MC in 24 h. The economic feasibility of the scaling-up of the hypothetical R-MBfR was also validated. Therefore, this membrane recycling could be a future green cost-effective alternative technology for MC removal.

  • 5.
    Sandh, Gustaf
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    El-Shehawy, Rehab
    Stockholm University, Faculty of Science, Department of Botany.
    Díez, Beatriz
    Stockholm University, Faculty of Science, Department of Botany.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Temporal separation of cell division and diazotrophy in the marine diazotrophic cyanobacterium Trichodesmium erythraeum IMS1012009In: FEMS Microbiology Letters, ISSN 0378-1097, E-ISSN 1574-6968, Vol. 295, no 2, p. 281-288Article in journal (Refereed)
    Abstract [en]

    Examination of the diurnal patterns of basic cellular processes in the marine nonheterocystous diazotrophic cyanobacterium Trichodesmium revealed that the division of cells occurred throughout the diurnal cycle, but that it oscillated and peaked at an early stage in the dark period. Transcription of the early cell division gene ftsZ and the occurrence of the FtsZ protein showed a similar diurnal rhythmicity that preceded the division of cells. DNA replication (dnaA gene transcription) occurred before the transcription of ftsZ and hetR, the latter encoding the key heterocyst differentiation protein. Transcription of ftsZ and hetR in turn preceded the development of the nitrogen-fixing diazocytes and nifH transcription, and were at the minimum when diazotrophy was at the maximum. The nifH gene transcription showed a negative correlation to the circadian clock gene kaiC. Together, the data show a temporal separation between cell division and diazotrophy on a diurnal basis.

  • 6.
    Vintila, Simina
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    El-Shehawy, Rehab
    Stockholm University, Faculty of Science, Department of Botany.
    Ammonium ions inhibit nitrogen fixation but do not affect heterocyst frequency in the bloom-forming cyanobacterium Nodularia spumigena strain AV1.2007In: Microbiology, ISSN 1350-0872, Vol. 153, no Pt 11, p. 3704-3712Article in journal (Refereed)
    Abstract [en]

    In the presence of ammonium ion, Nodularia spumigena strain AV1, a filamentous, heterocystous cyanobacterium isolated from the Baltic Sea, lost aerobic nitrogen-fixation activity while maintaining heterocyst frequency along the filaments. Real-time RT-PCR showed that the expression of nifH (encoding the dinitrogenase reductase component of the nitrogenase enzyme) was suppressed and the levels of NifH protein decreased dramatically in response to treatment with ammonium. On the other hand, ntcA (encoding the global nitrogen regulator in cyanobacteria) and hetR (the key regulatory gene in heterocyst differentiation) were expressed and their expression patterns were not affected by the treatment with ammonium. These data demonstrate that N. spumigena strain AV1 maintains heterocyst frequency along the filaments in the presence of ammonium and in the absence of detectable N2-fixation activity.

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